This application is for a competing continuation of a P30 Core Center, the Center for Drug Use and HIV Research (CDUHR). A continuation is proposed because (a) advancement in HIV research has led to an increasing focus on social-level influences to help understand HIV risk behaviors and transmission, and (b) the projects that comprise CDUHR provide a unique set of studies through which a range of social-level influences on HIV can be examined and integrated in a multidisciplinary environment. In addition, the need for a Core Center has increased: whereas the parent grant was initiated to provide support to 9 projects related to HIV and drug use, this continuation will provide a research infrastructure for 23 projects. The overarching scientific aim will be to enhance knowledge regarding social-level influences on HIV-related risk behaviors, prevention and transmission of HIV among drug users. CDUHR will provide support to increase the productivity of investigators, foster efficiency in project functioning, and enhance collaboration and synergy so that new research questions and studies will emerge which will exceed the accomplishments achievable by the simple summation of the activities of the individual projects. In addition, CDUHR will support the development of new knowledge, theory and methods and their dissemination to the field. The aims of CDUHR will be accomplished through 6 cores: (1) Social Theory Core -- furthers the use and development of supra-individual theory; (2) Research Methods Core -- enhances use of newly-emerging social-level research methods; (3) Statistics and Data Analysis Core fosters use of statistical methods that are appropriate for group and multi-level analyses; (4) Strategic Comparisons Core -- facilitates and undertakes studies with epidemics as the unit of analysis; (5) Dissemination and Training Core -- serves to maintain and advance knowledge and skills of staff and disseminate findings to service providers; and (6) Administration Core -- provides scientific leadership and ensures integration across Cores and synergy across projects and investigators.